Biomedical Engineering Reference
In-Depth Information
100
90
80
70
60
50
4.5
4.0
3.5
3.0
0
200
400
600
800
1000
h
max
(nm)
FIGURE 16.8
Human enamel elastic modulus
E
and hardness
H
data plotted
as a function of the maximum indentation depth
h
max
.
plateau only after the indent size exceeds that of the prism underneath the indenter tip. This phe-
nomenon is attributed to the continuously changing microstructure as probed by the indenter tip as
it penetrates deeper into the enamel. Upon its initial contact with the specimen surface, the indenter
tip only interacts with the prism immediately under it. However, as the penetration goes deeper, the
indenter begins to interact with the adjacent prism sheaths and prisms, and the measured mechanical
properties then reflect the total contribution of both the prisms and prism sheaths
[45]
. Despite the
fact that both bone and dentin are similar in composition, their deformation behaviors differ slightly
at the nanoscale. Theoretically, in these multicomponent materials, there should be a certain length
scale under which the constituents of the biological tissue no longer function together as a composite,
but instead, would behave as individual elements. Under this length scale, the scatter of the recorded
data obtained from repeated measurements on random sites would begin to increase drastically due
to the large difference in mechanical properties among the constituents. In bone, this value has been
estimated to be approximately 600 nm while, in dentin, this value was found to be in the region of
100 nm
[46]
. The arrangement of the constituent materials is therefore decisive to the mechanical
properties of the oral mineralized tissues.
16.4
CONCLUSIONS
Nanoindentation is a proven technique for characterizing the mechanical properties of materials at the
nano/microscale. However, accurate nanoindentation measurements on the oral mineralized tissues
cannot be achieved using the conventional technique developed for hard, synthetic materials. Major
areas for consideration when conducting nanoindentation on mineralized tissues include:
